1. Field of the Invention
The present invention relates to a particulate matter sensor and an exhaust gas purification apparatus.
2. Description of the Related Art
Conventionally, there is provided an exhaust gas purification apparatus, an exhaust gas purification method, and a particulate matter (PM) measuring method using a Diesel Particulate Filter (DPF) made of a porous ceramic material capable of collecting (removing) Particulate Matter (PM) including Carbon (C) as a main component of the Particulate Matter (PM) exhausted from a diesel engine. (Conventionally, there have been known an exhaust gas purification apparatus, an exhaust gas purification method, and a Particulate Matter (PM) measurement method) (see, for example, Japanese Patent Application Publication No.: 2008-101602A). In the exhaust gas purification apparatus, the Particulate Matter (PM) is gradually accumulated in the Diesel Particulate Filter (DPF) during continual use and the Diesel Particulate Filter (DPF) is periodically regenerated by burning and oxidizing the Particulate Matter (PM) in the Diesel Particulate Filter (DPF) to remove the Particulate Matter (PM). By regenerating the Diesel Particulate Filter (DPF), it becomes possible to prevent a clogging problem due to the accumulated Particulate Matter (PM) and continuous use of the Diesel Particulate Filter (DPF).
However, if the regeneration is performed when Particulate Matter (PM) is not so much accumulated, Particulate Matter (PM) may not be efficiently removed; namely, energy required for regenerating the Diesel Particulate Filter (DPF) may be wastefully consumed. On the contrary, if the regeneration is performed when there is too much Particulate Matter (PM) accumulated, an extra pressure loss may be generated between the upstream side and the downstream side of the Diesel Particulate Filter (DPF) in the exhaust gas flow passage in proportion to the delay in performing the regeneration process may increase the fuel consumption of the internal combustion engine. Therefore, to avoid this problem, it is thought to be required to always oxidize and remove the Particulate Matter (PM) in the Diesel Particulate Filter (DPF) (i.e., regenerate the Diesel Particulate Filter (DPF)) when an amount of particulate matter accumulated in the Diesel Particulate Filter (DPF) reaches a predetermined value (amount).
As a method of optimizing the timing for regenerating the Diesel Particulate Filter (DPF), there may be provided a measuring apparatus capable of measuring Particulate Matter (PM) accumulated in the Diesel Particulate Filter (DPF) by obtaining an amount of Particulate Matter (PM) accumulated in a detection filter provided in a secondary exhaust pipe bypassing a main exhaust pipe in which the Diesel Particulate Filter (DPF) is provided, the secondary exhaust pipe collecting a part of exhaust gas exhausted from the internal combustion engine as sample gas, where the amount of Particulate Matter (PM) accumulated in a detection filter is obtained based on a differential pressure between the upstream side and the downstream side of the detection filter.
In this measuring apparatus, the differential pressure is measured between the upstream side and the downstream side of the detection filter provided in the secondary exhaust pipe, and based on the measured differential pressure, the amount of the Particulate Matter (PM) accumulated in the detection filter is obtained (calculated). Then, based on the amount of the Particulate Matter (PM) accumulated in the detection filter, the amount of Particulate Matter (PM) accumulated in the Diesel Particulate Filter (DPF) is calculated. As a result, when determining that the amount of Particulate Matter (PM) accumulated in the Diesel Particulate Filter (DPF) exceeds a predetermined value, the regeneration of the Diesel Particulate Filter (DPF) is started. The entire contents of Japanese Patent Application Publication No. 2008-101602A, are hereby incorporated herein by reference.